Where is soffit venting necessary?
The December issue of Journal of Light Construction has an article featuring building techniques of four high performance builders. Three of the buildings pictured have truss roofs; one of those clearly has a ventilation channel from the soffit to the space above the insulation; one is unclear and one, a certified Passive House, clearly does not. There, the cellulose insulation is against the inside of the roof sheathing for what looks like 2′-3′. So my question is, in a vented attic over a very tight house, when is venting to the soffit necessary?